Enterprises in various industries have their data organized hierarchically. For example, a retail organization may have its sales data organized by states, regions, counties, and cities. When the data are organized in a hierarchical fashion, there are often accounting constraints that link series at different levels of the hierarchy. As an illustration, the sales of a particular product by a retail company is the sum of the sales of the same product in all stores belonging to the company. However, imposing such constraints during the forecasting process can be difficult or impossible. Therefore, the series are often forecast independently at different levels so that the resulting forecasts do not abide by the constraints binding the original series.